The present invention relates to metallurgy in general and to processes for the recovery of aluminum from its ores in particular.
In my prior U.S. Pat. No. 3,958,982, which is specifically incorporated by reference herein, and to which reference may be made for a full understanding of the background of the present invention, the shortcomings of the Bayer process were enumerated. Among these shortcomings is the fact that that process is only capable of extracting aluminum with maximum efficiency from hydrated aluminum oxide ore materials such as gibbsite and boehimite. Thus potential aluminum sources such as the kaolins or goethite are generally viewed as being unsuitable as starting materials in the Bayer process. In addition, any aluminum ore material containing in excess of 5% silica is generally considered unsuitable for use in the Bayer process due to the cost of the digestive removal of the silica. Finally, the very small particle size found in many bauxite ores results in the formation of "red mud" which is only difficultly separated from the alkaline aluminate liquor.
For these and other reasons my prior patent disclosed and claimed the use of various naturally occurring acids such as citric, tartaric and salicylic acids, in a process wherein the aluminum containing ore is treated with a solution containing one or more of such acids in order that the aluminum present in the ore may be complexed by the acid anions are carried into solution. This extraction is followed by filtration to remove the insoluble matter from the solution containing the complexed aluminum, and the filtrate is subsequently treated with a basic reagent whereby aluminum hydroxide is precipitated and removed from solution.
Despite the success of such process, there remains a need for a process which will accomplish a similarly efficient removal of aluminum from ores which are presently not amenable to the Bayer process, and also do so even more economically than my prior process.